Piezo transformers are used to convert voltages. Piezo transformers, called piezoelectric transformers or piezo transformers in English, have a primary side, to which a voltage or a current is supplied, and a secondary side, on which a current or a voltage is accessible.
Document U.S. Pat. No. 6,400,096 B1 describes a control circuit for a piezo transformer, which makes available a voltage for a fluorescent light source. For control purposes, a signal is accessible on the secondary side of the piezo transformer and thus, on the high voltage side.